For example, in a semiconductor device manufacturing process, devices such as transistors are formed on a semiconductor wafer (to be merely referred to as a wafer hereinafter) by various processes. If contaminants such as particles, organic contaminants, and/or metal impurities are present on the surface of the devices, it degrades the performance of the devices. Hence, the wafer must be cleaned for removing the contaminants. As such a wafer cleaning process, a process of storing a predetermined cleaning liquid in a cleaning tank and immersing a wafer in the cleaning liquid is employed often. This cleaning process is advantageous in that it can effectively remove the particles attached to the wafer.
The cleaning process using such a cleaning tank employs a cleaning apparatus in which a large number of chemical tanks for cleaning wafers in a batch manner using various types of chemical liquids, and a large number of purified water cleaning tanks are arranged alternately, thereby enabling a continuous batch process.
Demands for minimizing the space where the entire cleaning system is installed, decreasing the total cost, and the like arise recently, and a so-called one-path cleaning apparatus attracts attention (for example, see patent document 1). In a multi-tank cleaning apparatus as described above, chemical tanks and purified water cleaning tanks are arranged alternately to correspond to the respective processes. Unlike the multi-tank cleaning apparatus, the one-path cleaning apparatus has a function of supplying and discharging one or a plurality of chemical liquids and purified water to and from one cleaning tank, so that a plurality of processes are performed in the single tank. The one-path cleaning apparatus performs cleaning while supplying each chemical liquid into the chemical tank from a chemical liquid supply nozzle provided to the lower portion of the chemical tank and letting the chemical liquid overflow.
When performing the cleaning process in this manner, usually, the liquid surface is in contact with a gas in the tank. Hence, convection of the chemical liquid during the overflow undesirably dissolves the gas into the chemical liquid. When the gas dissolves into the chemical liquid in this manner, the cleaning process becomes less uniform. This problem is not limited in the one-path cleaning apparatus, but exists not a little in any cleaning apparatus that uses a cleaning tank.
Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 10-289894